Hobbing special-shaped toothed gears.



'IL i ZUSI.

ROBBIE@ SPEGXAL SSAPED TOQTHED SEARS.

APPLIOATIO FILED 1750.14, 1912.

Patente July 28, 191i N. E. ZUSl HOBBING SPECIAL SHAPED TOOTHBD GEARS.

APPLICATION FILED DEO.1'4.'1912. goggg Patented July 28, 1914.

2 SHEETS-SHEET 2.

NO RYAN El ZUSI, OF N-EVARK, NEW' JERSEY, .ASSIGNOR TO MEISSEL-BACH-CATUCCI BIFG. CO., Pl CDRPOBATIN OF NEN JERSEY.

l'GBBING SPECIAL-SHAEED TOTHED GEARS.

melissa.

Specification of Letters Patent.

Patented July 2S, i914.

"registers, etc.. hut so tar as l am aware no attempt has been made to cut such gears by the hohhing process. lt is Well known that the milling process as applied to gear cutting often results in imperfect gears, hecause of inaccuracy in indexing` due to the chilling of the cutter before the work is completed. the inaccuracy ot feeding' the.

Worlr to the cutter and many other reasons 'which are either impossihle or at least hard to account tor. For these reasons the manufacture ot regular shapec. gears is heing; done more and more extensively hy the hohhing process as its capabilities become more fully developed.

.ln the patent to Flin)7 Catucci, No. 978,113 dated Der. i5. 1910. is shown and described a gear cutting' machine designed for-cutting `D jears with regular or standard teeth, by means ol1 a hob of the usual type, and my inreut-ion has specific reference to said patent, and to the machine described therein, although it is to he understood that my special forms are capable of use in other hohbing gear cutters. and my process may he carried out with other iustrumentalities.-

When a particular form of gear, ratchet or other special toothed gear has heen decided upon, the prohleni is to determine the exact le in of the cutting edge ot' the hoh tooth lich will produce such special toothed gear. ln the solution-of the problem l have assumed the exact shape and number ot the teeth in a particular wheel, and proceed from such shape to generate the shape and 'i term ot the cuttingy edge oi the hoh tooth vwhich will iroduce such siecial forni l .1 or tooth. so that me resulting teeth shall all he te in shape and form, and the i. "l ."7 Lflll ,designed to out pointed ratchet teeth.

the art as the ,illustrates an end View of a hoh cutter dein thc gear shalln heg Velop the formed.

In the accompanying' drawings l have shown diagrammatically the method or" developing the shape and form of two such special forms; but l wish to be understood as in no Wise coniinin this development to these forms alone. f 'l e forms selected are, each extreme in its own direction, and inv practice have proven the most dillicult of all to produce. The development of the special forms shown will readily suggest to the designer the method of extending the process to any desired forni ofspecial tooth.

ln the drawings, Figure l illustrates diagrammatically several retrogressive positions of a ratchet tooth, the face of which is radial and the hack of which is straight, in connection with the corresponding positions of the edge and point of a heb cutter, Fic. 2 illustrates diagrammatically the supei. posed relative positions or" the retrogressing ratchet tooth, showing the method of depiocess by which such hohs may be vtelo )in 0' the curve of the cutter tooth to 'rencrate the straight hack et' the ratchet tooth. Fig. 3 illustrates the application of the process to the determinationo the shape of a hoh cutter tooth to produce what is known in double tooth ratchet. Fig. 4

signed for cutting the straight backed ratchet tooth. Fig. 5 illustrates a side View of the'sanie. Fig. 6 illustrates a sectional "iew of the ratchet toothed heb ,cutter and relative 'position of a single ratchet Wheel. Fig. 7 illustrates the end View of a double' toothed ratchet hoh cutter. Fig. 8 is aA side View of the same. Fig. 9 is a sectional view ot' the double ratchet hob cutter showing also the relative position or". the double ratchet. Fig. l0 is a partial side elevation of the hobhing gear cutter of Pliny Catilccis 1Patent No. 928,113, showing the method of cutting a gang of blanks.

Similar letters of reference refer to like parts throughout the specifica/,tions and drawings.

l'n the development of the process for laying out the shape of the cutting edge of a hoh for cutting the radial face straight hacked single ratchet, reference is made to Fics. let 0, l, 2, "4 l Wheel and O', l', 2', 3', 4f, etc., be the corresponding positions ofthe roots of such teeth, all of which are located upon the pitch circle X Y of the ratchet. The face of the ratchet tooth is assumed to loe radial as 0 N. Let the two lines' P Q and R S be assumed respectively as the pitch line and the locus of the progressive points of the tooth oi' the cutter. F rom the point O on the pitchcirele of the ratchet wheel, lav otli' on. the line R S the points 1, Q, 3", 4, 5", 13"", 7, etc., making their distances apart equal to 0, l, l', 2', etc. Erect a perpenrlicuh at each et the points including the perpendicular from the point 0, whichvin this case is also the vertical radius of the ratchet Wheel. If now the `ratchet wheel is assumed to revolve upon its center in the direction or the arrow, while the locus line S, travels in the same direct ion and tangent' to thc pi `h circle Y, at the extremity of the vertical radius, the root otl the tooth O. l, 3, 4, etc., will correspond successivel;T to the points l, Q, 3, etc.; in other words the point 0, 1"', 2, etc., may he assuni-:al as retrogressive positions ot the point; of the tooth of they rotating hoh cutter corresponding to the retrogressive positions ot the root of the ratchet tooth O', l. etc.

Referring now to if'ig. 2; lay ot linel P Q, and R S respectively as the pitch line and the locus of points ot'the teeth of the cutter respectively. Lay otlI upon the line R H the distance D E as the exact pitch of the ratchet, in this ease 0 N. Fircct D 'F and E G perpendicular to the line R S ai the points D and E respectively. The entire cutting edge of the hoh cutter tooth will now be contained in the rectangle D E (il F and the perpendicular l) F may be assumed to be that portion of the cutter tooth which will generate the radial tace 0 N of the tooth of the ratchet.

From a reference to Fig. l it will readily he seen that a point of the cutter tooth will come only in contact with the root of the ratchet tooth, when such point and root coincide at 0', O. From the point we draw a line l) 0 parallel to the hack of the tooth O, iu other words, draw the tooth 0 complete as it appears above the pitch line R Next draw the tooth l superposn the same on Fig'. 2 and making the hack o such tooth in the same relative position to the point D, that such tooth occupies in Fig. l with rcspect to the perpendicular from the point 1". Next superpose upon Fig. 2 the tooth 2 making it occupy the same relative position with respect to D, that it occupies in Fig. l with respect to the pointl 2". Next superpose upon Fig. 2 the tooth 3 making it occupy the saine relative position with respect to the point l) that the tooth 3 occupies with respect to the point 3 in Fig. l, and So on, superposing each of the relative positions of the teeth 4, .,"i, t3, 7, 8, E), l0, in Fig. 2 making such teeth occupy the saine relative positions with respect to the point D that they occupy in Fig. 1, with respect to successive points 4, 5, 6, etc. If now the curve is struck through the points of the teeth in Fig. 2 such cnrve will correctly delineate the locus of the point oi the ratchet tooth with respect to the advancing cutter tooth, hut since We are only interested in the generation of the hack of the tooth it will he readily seen that the backs of the superposed teeth in Fig. 'Il t'ornrthe envelop of the curve, drawn from the point D and running into the locus of the point of the tooth, it will also he seen the positions of the ratchet tooth at l) and 9 are entirely within this envelop; that the tooth at B'apparently is tangent to the curve of theenvelop, and that heyond S the envelop and the locus coincide. lhe curve of this envelop therefore determines the curve of the cutting edge of the hoh tooth lo generate the straight back of the ratchet tooth. By referring to the locus of the point of the tooth at T in Fig. 2 it will he seen that in this position the tooth merely touches the en velop at this point. The saine is true of the positions 5, 4, etc. T he envelop only touches the back of the tooth when it is in positions 7, 6, 5, 4, etc. The back of the ratchet tooth begins to generate in its true forni at the point where the locus of the advancing tooth coincides with the envelop curveand from that point the hack of the tooth may he assumed to roll u on the envelop curve up to the point D. n practice, therefore, it is only-necessary to continue the envelop curve up to the point where such curve unites with the locus ot' the point of the tooth.v and such curve may then he continued right on up a. shown in Fig. 2 to the line. i Q so that after the point of the toot-h leaves the curve it is entirely free fromA Contact with the cutter.

This is as it should he, tor a tcr the point oi!- the tooth has heen,generated, there is no necessity t'or further nnehanical operation upon it. The continuation ol' the enveloping curve to the pitch line. I Q alsoA overcomes the nn.cl1aniea l ditiiculty ot forming the curve in the cutter tooth accurately beyond the point where the curve and the locus oi the tooth pointcoinciile. ln other words, hy cuttinw away the metal between the point ll, and tie point G, plenty of clearncss is lett for the progressive travel of the point of the ratchet tooth.

lVe have, therefore, the curve D H as the correct shape of that edge ot the cutter tooth which will generate a straight hacked ratchet tooth. The edge of the tooth which zjenerates the radial tace .O N, of the tooth must/obviously coincide with such radial t'acc at the vertical radius O C, at which point the ver)Y last shaving of metal is re* moved and the face is completed. The conalogene `upon the hob, it is readily seen that the tooth just formed by the cutter tooth F G H would 'be completely destroyed. tis, there` fore, necessary that the last cutter tooth on the hub should be located at a point where the point of such cutter tooth D coincides with the root of the tooth in order that the shape of the tooth may be preserved,

this feature will be explained, `hereinafter,V

in the specific description of the hob itself.

The above description of the generation of lthe contour of the hoh tooth applies to one oi: the extreme forms of my invention. The other extreme is the form or" the hob tooth designed .to generate What is known as the double ratchet. All other forms of gear teeth may he included between these two extremes. ln the generation of the form of cutter tooth to cut the double ratchet, the

'same process of retrogressive super-position of a contour of the tooth upon the Wheel to be cut is utilized for, determining the contour of the cutting teeth. ever, as this process of retrogressive superposition has been fully explained above, it is deemed unnecessary to repeat it with special application to the forni of cutter tooth to cut the double ratchet. ln this case, the contour of the cutting edge of' the tooth instead of being a curved envelop becomes a broken line.

Reference is now made to. Figr. ln this case the sides of the double ratchet tooth, instead of being radial are tangential to circle which is concentric with the center of the ratchet. For example, the faces of the teeth 20 and 2l are tangential to theA circle iis above explained, the reason set forth above for locating the last tooth of the cutter in the vertical radius applies in the present case and the shape oi such tooth must be substantially the shape of the notch between the adjacent teeth of the ratchet. inasmuch as the last tooth of the cutter removes the nal shaving which come pletes the faces of such teeth, We may start with a 'cutter' tooth Whose cutting edge is substantially the shape oi" this notch or groove. liet 2e be such cutter tooth. lf now that tooth be located axially upon the vertical radius 26 of the double ratchet, it will appe as shown i Tyig with the l of such cutwi tooth coincidott tivo "I ratchet f. M adjacent inasmuch, how# teeth 2O and 2l. and the pitch of the double ratchet will obs viously be the same, but it is noted ironia reference to Fig. 3 that with the tooth 24 in the position shown the corresponding tooth 2?' in the next helix of teeth on the cutter would interfere with or cut away .a portion of the material which would form the tooth 2l, unless some special provision Were made, to avoid such cutting away. l provide for this by changing the pitch of the cutter teeth upon one side, so that'it will not interfere with the adjacent point of the ratchet tooth 2l as clearly shown in Fig. 3. Now since the cutter is revoluble we have the exact shape oi' the tooth 24 and the tooth 27 as being the corresponding teeth in successive helices upon the cutter. All of the teeth surrounding the helix, of Which tooth 24 is the first tooth, Will gradually vary in Width until such helix runs into the helix of Which tooth 2T is the first tooth; theoretically the next tooth :28 of the cutter would be correspondingly reduced in thickness and the tooth in the helix oi which 27 is the first tooth would gradually diminish in thickness around the body of the cutter until they approach the thickness of tooth 2S; but in practice only about two helices of teeth on the cutter are active, so that the 'tapering of the helix 0I" the teeth need not be carried beyond the second or third helix.

inasmuch as the tooth 24 is the last to act upon the groove between the teeth 2O and Qlit is quite obvious that, because of the faces oi' such teeth 20 and 2l being tangent to the circle 22, the cutting edge of the tooth 24 would not cut completely down to the root of the K tooth 2l. clearly shown by the fact that the point line of the cutter teeth is tangent to the pitch circle or4 the ratchet. It it is necessary that this slight excess of material be removed that the ratchet may operate successfully the cutting edge of the tooth 24 may be extended out so that its lower cutting edge Will coincide with the pitch line of the ratchet.

The pitch of the cutter This is quite A l have shown this more fully in. connection With the cutter tooth 27, where the outline at the point of the tooth, vas at 29, illustrates the exact shape'oi' the tooth, to remove the slight portion of metal located right at the root of the advancing tooth oi the ratchet. ln practice, however, this would form no obstacle to the usual operation of the ratchet tooth andthe points of all of the teeth in the cutter. may coincide with the surface of an enveloping cylinder.

In Figs. l and 5 I have shown the form which a hob cutter for cutting straight backed single ratchets will take. It Will be observed in Fig. 5 that the tooth 30, is the last cutting tooth of the helix which is designed to remove the very last shavingof a tooth such as 3i, (Fig. o) to forni removed from the cutter body and left blank as at 33 upon the body of the cutter, as shown in Fig. 5.

In Figs. 7 -and 8 I have shown the form of the cutter designed for generating the double ratchet as shown in Fig. 9. It will be observed in this case that tooth 34 is the last cutting tooth of the helix of teeth and that as the helix progresses around the cy lindrical body they are successively narrower, for the reason above stated. It is understood that the tooth in advance of tooth 30 and tooth 3l serves the purpose of removing the shavings of metal from the blanks but that it is in each case the last tooth as 30 or 34 which removes the very last shaving of metal to complete the form of the back of one tooth and the face of the next successive tooth.

In the practice of my invention a plurality of disks 35 is mounted upon and firmly secured to a mandrel 36 and the mandrel is then mounted between the centers of the hob cutting machine, for example, that shown and described in the above named patent to Pliny Catucei. The cutter 37 is mounted upon the cutter shaft 38 which is in turn carried in the bearings 39 of the vertical stanchion 40. The cutter shaft 38 may be raised and lowered by means of a vertical feed screw 41 which is operated by means of the crank 42. The mandrel 3G is rotated at a predetermined speed by means y ot' the change speed gears 4-3 and the vertical stanchion 4t() is fed by the proper feeding mechanism 44 as fully described iu the above named patent to Pliny Catucci. llowever, the cutting machine forms no part ot' my invention and I have only illustrated so much of the cutting machine of the Catucei patent to show the method of using all forms ot' hob cutters, as may be necessary to gain a full understanding of the same.

In each of the specially constructed hobs, it will be noted that the cutting edges of the teeth are in radial planes' that is to say,- all lie in planes which pass through, the axis ot the cutter;` and that the backs of such teeth are relieved; that is to say, the backs of the teeth lie in circles,'each ot' which is eccentric tothe pitch line of the teeth. 'By so constructing them, the radial sections ef the teeth are always the same, so that the, teeth may be sharpened by running a special 'shaped grinding wheel in the grooves which separate the successive teeth in their respective helices.

It will thus be seen that I have developed a new process for generating the teeth of a hob gear cutter for cutting special toothed gears, and this process consists generally in assuming the shape of the tooth of the special gear and then proceeding retrogressively with various positions of the tooth, so as to form a corresponding series of superposed tooth contours, and through such a series of contours the enveloping curve or broken line as the case may be is delineated.

This enveloping curve must therefore be l the correct shape'of cutting edges of the helical row of teeth upon the hob cutter. The final step consists in removing all of the teeth of the last helix excepting that which takes 'the last` shaving from, and develops the final shape of the tooth of the special gear. In practice the work piece is set with special regard to this last tooth, as tooth 30 of the straight backed single ratchet, or tooth 34 of the double ratchet Wheel.

I have not shown those forms of cutter teeth which would come between the extremes shown in the drawings and described above, as it is obvious that the correct form of cutter tooth may be readily developed, when only the special form of the toot upon the wheel is known.

I claim:

1. A hob cutter having a cylindrical body lwith a helical ron7 of cutting teeth upon said body, said helical row beginning with the first tooth having the contour of its cutting edge complete.

2. A hob cutter having a cylindrical body, and a helical row ofcutting teeth thereon, said row beginning with the tooth Whose cutting edge is Of complete contour and whose cutting edges lie in radial planes.

3. A hob cutter having a cylindrical body and a helical row of cutting teeth thereon, the first tooth of which is of complete contour, said row of teeth varying in contour progressively throughout the heliX from said first tooth.

4. A. hob cutter having a cylindrical body and a helical row of teeth, with the contours of the cutting edges of said teeth varying progressively throughout the length of the helix.

A hob cutter for cutting ratchet teeth having a cylindrical body and a helical row of teeth thereon, the contour of whose cutting edges is determined by the envelop line generated by the retrogressivf,l super-position of a complete ratchet tooth of the form to be cut relative to the corresponding position of some definite point in the cutter tooth.

6. A hob cutter for cutting ratchet teeth having acylindrical body and a helical row of teeth thereon, the contour of Whose cutsus*l ting edges is determined`v by the envelop line generated by the ret-regresen@ superposition of e. complete ratchet tooth of the yforni le he out', relative to the Corresponding position of Some definite point in the cut-teitooth, said helical row of teeth beginning with a tooth, the contour of whose cutting edge is full or complet/e,

'7. A. hoh Cutter having a cylindrical body and a helical row of Cutting teeth thereon, the Cutting edges of which lie in radial planes, and having all mutilated or incomplete teeth removed from seid cylindrical body et. the beginning of the helix.

and lies in a. plane radial to the cylindrical 20A body.

In testimony whereof I have hereunto set my hand this 6th day of December, 1912.

NORMAN E. ZUSI.

In presence of* PLINY CATUCCI. LOUIS M. SANDERS. 

